Vladimir Putin does not have a "serious" injury, Dmitry Medvedev, the Russian prime minister, has said, as rumours continue to swirl over the president's health.

Mr Medvedev did not go into detail, saying "I'm not a doctor", but he indicated that Mr Putin had suffered a minor sports injury. "Everybody has the right to look after their health," he said, speaking to reporters from Finland before a visit there.

Mr Putin cancelled and postponed a series of recent foreign trips leading to speculation that he was unable to withstand long flights.

His spokesman said last month that he strained a muscle playing sport but did not explain exactly how it happened.

Mr Medvedev said Mr Putin, like other leaders, "needs to do a lot a lot of sport to keep in shape. In any case, he's alive and well and, thank God, everything is fine with him." He added: "It's nothing serious. Every person has some trifle which they need to take care of."

Russia media earlier suggested that Mr Putin may have aggravated an old back injury when he flew a motorised hang glider to guide a group of Siberian Cranes hatched in captivity toward their southern wintering grounds in September.

Vedomosti newspaper cited one source then as saying that Mr Putin was undergoing medical treatment on his back and doctors' "main recommendation" was to avoid flying, which could have a negative effect on his spine.

The Kremlin denies the injury was connected to the birds stunt. A more mundane explanation is that the president hurt himself while riding, practising judo or playing ice hockey, three of his pastimes. A documentary about the leader shown on Russian television to coincide with his birthday last month showed him limping. He was also limping noticeably at an economic summit in the Russian Far East two months ago.

Mr Putin nonetheless was photographed with Nicolas Sarkozy, the former French president, in Russia on a private visit. The Russian president referred to Mr Sarkozy as "Dear Nicolas".

Mr Putin frequently stays in touch with former colleagues even after they have left office, most notably former Italian Prime Minister Silvio Berlusconi.